1. Field of the Invention
The present invention relates to mobile communications, especially to a method and an apparatus for performing switching in a mobile communication system.
2. Description of the Related Art
An existing structure of the 3rd Generation Mobile Communication System Partnership Project (3GPP) is shown in FIG. 1.
User Equipment 101 (UE) is a mobile terminal device used to receive data. Node B 102 is a node for radio receiving/transmitting in an Radio Network Subsystem (RNS). Control Radio Network Controller 103 (CRNC) is a radio network controller that controls Node B directly. An interface between a radio network controller (RNC) and the UE is provided via an wireless interface. A Serving Radio Network Controller 104 (SRNC) is used as the RNC to control bearer information such as a Radio Resource Control (RRC) information. The interface between SRNC and CRNC is an Iur interface. Gateway General Packet Radio Service (with General Packet Radio Service referred to as GPRS) Supporting Node 106 (with Gateway GPRS Supporting Node referred to as GGSN) and Service GPRS Supporting Node 105 (SGSN) provide routing for data transmission. An interface between SGSN and RNC is a lu interface. An External Public Data Network (E-PDN) 107 for providing data resources.
A system structure of Service Architecture Evolution (SAE) is illustrated in FIG. 2. Referring to FIG. 2, UE 201 is a terminal device used to receive data. EUTRAN 202, also called evolved Node B (eNB), is a radio access network of the LTE SAE, for providing an interface through which a Long Term Evolution (LTE) mobile station will access the radio network. Through the interface S1, eNB 202 connects to the mobile station Mobility Management Entity (MME) 203 and the user plane entity Serving Gateway (Serving GW) 204. MME 203 is used for managing a mobile context and a session context for the UE, and saving user security information. Serving GW 204 primarily provides a function of user plane for delivering information from user. An interface S1-MME is used for establishing radio access bearer for UE and forwarding messages from the UE 201 to the MME 203 through a wireless access network. The combined function of MME 203 and Serving GW 204 is similar to that of the original SGSN 206. Both the MME and the Serving Gateway can be located at the same physical entity. Public Data Network (PDN) Gateway 205 is used for functions like accounting, legal monitoring, etc. Both the Serving Gateway and the PDN Gateway can be located at the same physical entity. SGSN 206 provides routing for data transmission for existing Universal Mobile Telephone Service (UMTS). The existing SGSN finds a corresponding GGSN according to an Access Point Name (APN). A Home Subscription Sub-system (HSS) 207 is provided for the UE, for storing user information that includes a current location of the UE, an address of the serving node, security related information for the user, and an activated Packet Data Protocol (PDP) context for the UE. Policy and Charging Rules Function (PCRF) 208 provides a Quality of Service (QoS) policy and accounting rules through an interface S7.
In general, a user data stream arrives at the Serving GW 204 through PDN Gateway 205. Then, through the GPRS Tunnel Protocol (GTP) channel, data is transmitted by the Serving Gateway to the eNB where the UE locates, and transmitted by the eNB to a corresponding UE.
FIG. 3 shows a structure of interface S1 in SAE, where Evolved Packet Core (EPC) is the LTE core network. Here, each eNB 301 connects with several MMEs 312 in the MME pool. Each eNB 301 also connects to several S-GWs 311 in the S-GW Pool.
A Home Network B (HNB), which includes 3G HNB, LTE HNB and HNBs for the other access systems, refers to a Node B applied in a home. It also can be applied in sites such as a university, a company and so on. HNB is Plug-and-Play. HNB includes an open-typed HNB and the close user group-typed HNB. A difference between the close user group-typed HNB and a common macro eNB lies in that usually not all UE can access the HNB. For example, only the UEs in the home of a user or other UEs specifically allowed to access the HNB can access the corresponding HNB. For the HNB in a company, only a company's staff and allowed partners can access the HNB. The HNB group, for example, an HNB in a company, bearing the same access subscriber cluster is called a Closed Subscriber Group (CSG).
The structure of the 3G HNB is illustrated in FIG. 4. A UTRAN 400 includes a 3G HNB 401 and a 3G HNB GW 402. The HNB and the HNB GW form an HNB RAN. 3G HNB performs the functions of original NodeB and some functions of RNC, such as RRC, RLC, MAC, etc. The 3G HNB GW is a node connecting to the core network, including a function of NAS Node Selection Function (NNSF). The interface between HNB and HNB GW is the Iuh interface. 3G HNB GW accesses the core network through the lu interface.
No conclusion is made on the structure of LTE HNB (HeNB). A solution is that MME and S-GW are directly connected to the HeNB. Another solution is that a structure similar to 3G HNB, and HeNB accesses the core network through the HeNB GW.
When UE switches between eNBs, an existing MME relocation process is illustrated in FIGS. 5A and 5B. If no relocation is performed by the Serving GW, the source Serving GW in FIG. 5A functions as a target Serving GW.
In step 501, the source eNB 520 decides to initiate an S1 switching process. This process can be triggered when no X2 interface exists between the source eNB 520 and the target eNB 530, triggered by an error indication from the target eNB 530 when an unsuccessful X2 switch is performed, or triggered by the dynamic information obtained by the source eNB 520.
In step 502, the source eNB 520 transmits a “Switching Request” message to the source MME 540. The message includes an indicator indicating whether data can be directly forwarded between the source eNB 520 and the target eNB 530. The “Switching Request” message includes message elements of:                MME UE S1AP ID (MME UE S1 application layer identifier).        eNB UE S1AP ID (eNB UE S1 application layer identifier).        Switch type, including IntraLTE (within LTE), LTE to UTRAN (from LTE to UTRAN), LTE to GERAN (from LTE to GERAN).        Cause for switching.        Source ID. The same method for setting the source ID can be applied in the configuration of both the source ID and the target ID. For example, the ID may include a TAI (Tracking Area Identity) and a unique eNB ID in a Public Land Mobile Network (PLMN), i.e. a global land mobile network, or a PLMN ID, which is a unique eNB ID and the MME group ID under PLMN.        Target ID, which can be either the PLMN ID or the unique eNB ID under PLMN. For the sake of routing between MMEs, the target ID can also include the TAI and the MME group ID. If the TAI is included for the sake of routing between different MMEs, the target ID includes the TAI and the unique eNB ID under PLMN, since the TAI has already contained the PLMN ID.        Availability on direct data forwarding.        Intra-LTE-switch information list request, which is enabled when there happens IntraLTE switching, and includes a transparent container from the source eNB to the target eNB.        LTE-UTRAN-switching information list request, which is enabled when LTE to UTRAN switching occurs.        LTE-GERAN-switch information list request, which is enabled when LTE to GERAN switching occurs.        
In step 503, the source MME 540 selects a target MME 550 and transmits a “Forward relocation request” message. Detailed description on MME selecting is omitted here for conciseness. The “forward relocation request” message includes the MME UE context. The MME UE context includes a PDN GW 580 address and TEIDs for uplink data transmission, which corresponds to the interfaces S5 and S8 of GTP, and a Serving GW address and TEIDs for uplink data transmission. The message also includes an indicator indicating whether data can be forwarded directly or any bearer has been established in the source side for indirect data forwarding. The message further includes a switching type, a switching cause, and a container from source eNB 520 to target eNB 530 since it is the switching inside the LTE.
In step 504, the target MME 550 verifies whether the source Serving GW 560 can still serve the UE 500. If not, the target MME 550 selects a new Serving GW, a detailed description of which is omitted here for conciseness. The target MME 550 transmits an “establishing bearer request” message to the target Serving GW 570. If the source Serving GW 560 still serves for the UE 500, it also acts as the target Serving GW. In this case, the message in this step is not necessary. The “establishing bearer request” message includes a bearer context, such as the PDN GW address and the TEIDs, which corresponds to interfaces S5 and S8 of GTP. The target Serving GW allocates the S-GW address and TEIDs for uplink data transmission through interface S1.
In step 504A, the target Serving GW 570 transmits an “establishing bearer response” message to the target MME 550. This message includes a Serving GW address and uplink TEIDs.
In step 505, the target MME 550 transmits a “switching request” message to the target eNB 530. This message includes the Serving GW address and the uplink TEIDs. After the target eNB 530 receives this message, it establishes the UE context including the bearer and the security context. In the message, the switch type is set as IntraLTE. The “switching request” message includes information elements of: MME UE S1AP ID (MME UE S1 application layer identifier); Switch type, including IntraLTE (within LTE), LTE to UTRAN (from LTE to UTRAN), LTE to GERAN (from LTE to GERAN); Cause for switching; SAE bearer list to be established; intra-LTE-switch (within LTE) information list request, which is enabled when there happens IntraLTE switching, and includes the transparent container from the source eNB to the target eNB; UTRAN-to-LTE switching information list request, which is enabled when there happens UTRAN to LTE switching; GERAN-to-LTE switch information list request, which is enabled when there happens GERAN to LTE; a serving PLMN; and a switching constraint list.
In step 505A, the target eNB 530 transmits a “switching request ACK” message to the target MME 550. The message includes the address and the TEIDs allocated by the target eNB 530 for downlink data transmission through interface S1.
In step 506, if an indirect data forwarding mode is applied here, the target MME 550 specifies forwarding parameters for the target Serving GW 570.
In step 507, the target MME 550 transmits a “forwarding relocation response” message to the source MME 540. The message includes an indicator indicating whether any change takes place in the Serving GW. If a change does take place, a new Serving GW is indicated. If the indirect data forwarding mode is applied here, the message also includes the Serving GW address and the TEIDs for data forwarding.
In step 508, if the indirect data forwarding mode is applied here, the source MME 540 updates the source Serving GW's channel for data forwarding. If the Serving GW has been relocated, the “establishing bearer request” message also includes an index of the channel between the source and the target Serving GWs.
In step 509, the source MME 540 transmits a “switching command” message to the source eNB 520. The message includes a target address and TEIDs allocated by eNB for data forwarding. The switch command includes the information elements of: an MME UE S1AP ID, i.e. MME UE S1 application layer identifier; an eNB UE S1AP ID, i.e. eNB UE S1 application layer identifier; a Switch type, including IntraLTE (within LTE), LTE to UTRAN (from LTE to UTRAN), LTE to GERAN (from LTE to GERAN); a bearer list for data forwarding; an SAE bearer list to be released; an Intra-LTE-switch (within LTE) information list request, which is enabled when there happens IntraLTE switching, and includes the transparent container from the source eNB to the target eNB; an LTE-UTRAN-switching information list request, which is enabled when LTE to UTRAN switching occurs; and an LTE-GERAN-switch information list request, which is enabled when there happens LTE to GERAN.
In step 510, the source eNB 520 transmits the “switching command” message to UE. This message includes information on radio resource configuration of the target cell.
In step 511A, for the bearer for data forwarding, the source eNB 520 begins to forward downlink data to the target eNB 540. Here, either a direct data forwarding mode (step 511A) or the indirect data forwarding mode (step 511B) can be applied here.
As shown in FIG. 5B, in step 512, after UE 500 is synchronized to the target cell, the UE 500 transmits a “switching ACK” message to the target eNB 530. The target eNB 530 can transmit the forwarded downlink data to UE 500. Similarly, the UE 500 can transmit the uplink data.
In step 513, the target eNB 530 transmits a “switching notification” message to the target MME.
In step 514, the target MME 550 transmits a “forwarding relocation complete” message to the source MME 540. The source MME 540 transmits a “relocation complete ACK” message to the target MME 550.
In step 515, the target MME 550 transmits an “updating bearer request” message to the target Serving GW 570. The message includes an eNB address and the TEIDs allocated by the target eNB 530 for downlink data transmission through interface S1, and the PDN GW address and the TEIDs for uplink data transmission (this case corresponds to the interfaces S5 and S8 of GTP).
In step 516, if the Serving GW is relocated, the target Serving GW 570 allocates addresses and TEIDs to PDN GW 580 for downlink data transmission. The target Serving GW 570 transmits the “updating bearer request” message to PDN GW 580. The message includes the Serving GW address and the TEIDs.
In step 516B, PDN GW 580 updates the context information and transmits an “updating bearer response” message to the target Serving GW 570. PDN GW 580 begins to transmit downlink data to the target Serving GW 570. If the Serving GW has not yet been relocated, the message in this step is not necessary. Serving GW directly transmits data to the target eNB 530.
In step 517, the target Serving GW 570 transmits the “updating bearer response” message to the target MME 550. This message includes the PDN GW address and the TEIDs corresponding to interfaces S5 and S8 of GTP.
In step 518, UE 500 initializes a Track-Area-Updating (TAU) process, regarding which a detailed technical description is omitted here for conciseness. The target ID in the “switching request” message of step 502 of FIG. 5A facilitates the MME to obtain a downstream node, e.g., the HeNB or HeNB GW.
However, a length of the HeNB ID or the HeNB GW ID possibly differs from that of the macro eNB, and the information on adjacent HeNBs is not saved in the macro eNB. When the target cell is a CSG cell, the manner of making the macro eNB learn about the eNB type or eNB ID of the target cell will not be solved. Thus, the process of switching from a macro eNB to an HeNB can not be implemented.